In general, a catalyst for ethylene polymerization and copolymerization containing magnesium has been known to have an extremely high activity, serve to prepare a polymer with a high bulk density, and be suitable for liquid and gaseous polymerization.
Ethylene liquid polymerization refers to a polymerization process performed in the medium such as bulk ethylene, hexane or iso-pentane. Catalysts used in this process feature the high activity, the bulk density of the prepared polymer and the content of the low molecular weight soluble in the medium. Of these features, the activity of catalysts is one of the most important characteristics. Moreover, the molecular weight distribution is an important variable to determine the property of the ethylene polymer, and the broad molecular weight distribution is an important characteristic depending on use of the polymer.
As the prior art, a catalyst for olefin polymerization based on titanium containing magnesium and a process for preparing the same have been reported. A method using a magnesium solution has been well known as the process for preparing olefin polymerization catalysts to obtain a polymer having a high bulk density.
The U.S. Pat. No. 4,330,649 discloses a method for obtaining a magnesium solution by the contact reaction of a magnesium compound with an electron donor such as alcohol, amine, organic carboxylic acid and aldehyde under the presence of a hydrocarbon solution. Also, a method for preparing a magnesium-supported catalyst by reacting the liquid magnesium solution with a titanium compound containing halogen such as titanium tetrachloride and electron donors such as organic acid ester, organic acid halide, anhydrous organic acid has been well known. Although the above-described catalyst provides a high bulk density, it has disadvantage that its catalytic activity is required to be improved, and the process for preparing it is performed through many steps.
The U.S. Pat. No. 5,459,116 discloses a method for preparing a supported titanium catalyst by the contact reaction of a titanium compound with a magnesium solution containing ester having not a silicon compound but at least one hydroxyl group as an electron donor. The polymer by the catalyst has a high bulk density and an ultra high molecular weight, but the activity of the catalyst is required to be improved.
The U.S. Pat. No. 4,843,049 discloses a method for preparing a catalyst having a high titanium content by reacting titanium alkoxides with magnesium chloride-ethanol support manufactured by a spray drying method and then reacting diethylaluminum chloride or ethylaluminum sesquichloride. The method provides a high bulk density, and the activity of the catalyst increases as the titanium content becomes higher. However, the catalytic activity is extremely low so that it is required to be improved.
The U.S. Pat. Nos. 4,847,227, 4,816,433 and 4,829,037 disclose a method for preparing a catalyst by reacting a titanium chloride compound with electron donors such as magnesium alkoxide, dialkyl phthalate, dialkyl terephthalate under the presence of aromatic hydrocarbon solvent.
The U.S. Pat. Nos. 4,970,186 and 5,130,284 disclose a method for preparing a catalyst for olefin polymerization providing an advantageous polymerization activity and an improved bulk density of an obtained polymer by reacting a titanium chloride compound with electron donors such as magnesium alkoxide and phthaloyl chloride.